This invention is related to the field of digital signal processing, and more particularly to the acquisition, processing and storage of video data and Program Guide Information derived from input data encoded in variable broadcast encoding formats.
In video processing and storage applications, digital video data is typically encoded to conform to the requirements of a known standard. One such widely adopted standard is the MPEG2 (Moving Pictures Expert Group) image encoding standard, hereinafter referred to as the xe2x80x9cMPEG standardxe2x80x9d. The MPEG standard is comprised of a system encoding section (ISO/IEC 13818-1, Jun. 10, 1994) and a video encoding section (ISO/IEC 13818-2, Jan. 20, 1995), hereinafter referred to as the xe2x80x9cMPEG systems standardxe2x80x9d and xe2x80x9cMPEG video standardxe2x80x9d respectively. Video data encoded to the MPEG standard is in the form of a packetized datastream which typically includes the data content of many program channels (e.g. content corresponding to cable television channels 1-125). In order for a decoder to decode the packetized datastream and to recover the video data content of selected program channels for display, for example, the individual packets that comprise the selected program channels must be identified and assembled.
In order to recover the content of selected program channels, information in a Program Guide is used in identifying and assembling individual data packets that constitute the selected programs. For this purpose Program Guide data is acquired from the program datastream that is input to a video decoder. The Program Guide data is formed into a Master Program Guide (MPG) sufficient to decode the selected programs. Once it is formed, the MPG may be used to decode the selected programs or it may be transmitted along with the data content of the selected programs to another application device. However, in some video transmission systems, it is necessary to acquire and form the MPG from Program Guide data encoded in variable broadcast encoding formats.
Variable broadcast encoding formats are used in wireless terrestrial video broadcast systems to selectively provide enhanced levels of broadcast signal noise immunity. However, a broadcast encoding format that provides enhanced noise immunity also requires increased transmission bandwidth. An example of a system that uses variable broadcast encoding formats is the proprietary Multipoint Microwave Distribution System (MMDS) which uses a xe2x80x9cline-of-sightxe2x80x9d transmission system. In such a system, an encoding format that provides a broadcast signal with a higher degree of immunity to noise also incurs a higher error correction coding overhead and consequently requires greater transmission bandwidth. Similarly, for a fixed transmission bandwidth, providing a broadcast signal with a higher degree of noise immunity reduces the information throughput that may be attained. Further, the encoding format used may be varied on a temporal or geographical basis to accommodate variations in reception conditions associated with atmospheric or landscape features.
The variation in broadcast modulation and error correction coding format and the associated required transmission bandwidth presents problems to a video receiver both in decoding the variable encoding formats and in acquiring a compatible MPG. These problems are addressed by a system according to the present invention.
The use of variable broadcast encoding formats may result in a variation in the transmission bandwidth available for program data content. The inventors have hereby recognized that the number of program channels that are transmitted using variable broadcast encoding formats may be changed in conjunction with encoding format. Further, the number of program channels may be varied both over time, and with geographical broadcast area.
The inventors have further recognized that it is desirable for a receiver system to be capable of adaptively receiving variable broadcast encoding formats and a variable number of program channels. This allows the signal noise immunity of the broadcast system to be tailored to the requirements of a particular broadcast area. The receiver may be configured to provide higher broadcast signal noise immunity in a particular broadcast area where reception conditions are impaired due to hilly terrain, for example.
A disclosed receiver system automatically adaptively tunes to broadcast signals that are variable in: a) the number and the frequency allocation of the channels that are transmitted, b) the signal coding type e.g. trellis or non-trellis coded, and c) the modulation format e.g. formats using symbol constellations of 64 or 256 elements.
In accordance with the principles of the present invention, a system receives a digital bitstream representing video information encoded in one of a plurality of different formats, and transmitted on one of a plurality of transmission channels. In the system, a method for acquiring data transmitted on a transmission channel involves selecting a transmission channel from the plurality of channels and selecting a modulation format. The method also involves tuning to receive the modulation format and determining whether valid data is being received on the selected transmission channel. The method steps are repeated.
In a feature of the invention, the method for acquiring data transmitted on the transmission channel involves selecting a coding type and tuning to receive the coding type.
In another feature of the invention, the method for acquiring data involves repeating the method steps until valid data is received, capturing program guide information on the selected transmission channel, and re-tuning to receive a transmission channel in response to the program guide information.